1. Field of the Invention
The present invention relates generally to the field of snorkels for diving and the like, and more specifically to dry snorkels which are designed to prevent water from entering a snorkel tube while the snorkeler is submerged.
2. Prior Art
When floating up after diving down, the diver is often in urgent need of breathing air in quantities as soon as possible but he or she has to first perform "purging the snorkel" forcefully to clear water out of the snorkel after the snorkel top raises beyond the water surface. This is often difficult because the snorkeler may not have sufficient air remaining in his or her lungs required to purge the snorkel completely.
Oftentimes, the snorkel is insufficiently cleared of water during purging which results in restricted breathing and gurgling water or in worse cases, water inhaled into the mouth and lungs causing choking. Even if the snorkel has a purge valve in the lower housing, if water remains after the initial purge, it is especially difficult to purge out the remaining water because the next forceful blast of air will more easily rush past the water out the snorkel tube top rather than opening the purge valve because significant water pressure holds the purge valve shut. Therefore, if the first purge of air does not adequately clear the snorkel of water, then usually the snorkeler must raise their head above the water, remove the snorkel from their mouth, and manually drain it. This is very inconvenient.
In a conventional snorkel, the opening at the top end thereof is only about 10-15 cm above the water level when the diver is floating. The tail end communicates with the diver's mouth, so a trifling carelessness (such as the snorkel is inclined) or a wave on the water surface may cause water to flow into the snorkel mouth and lead to the danger of swallowing water or choking the bronchia with water.
After purging water from a conventional snorkel, there is usually some residual water remaining in the lower housing. Oftentimes the amount of this residual water is sufficiently little so that the snorkeler may breathe past without significant "gurgling" noises, but is still enough to effectively reduce the breathing passage size such that breathing resistance is increased.
There have been so-called "dry snorkels" made in the past that were designed to keep water from entering the snorkel in the first place. The principle is that when the snorkeler descends below the water, a floating component of the snorkel shuts the upper opening to prevent water from entering the snorkel tube; assuming that the snorkeler keeps the mouthpiece sealed inside their mouth. The first such design had a snorkel tube that curved 180 degrees so that the opening faced the water surface. A ping pong ball (usually) was suspended in a cage below the open snorkel tube. When the snorkel submerges, the ball floats upwards sealing the snorkel tube. The problems with this design are general bulkiness and unattractiveness, and there is a flow restriction caused by the 180 degree bend in the snorkel tube. The general shape is poor for hydrodynamics and tends to catch on things such as seaweed. Also, if the snorkel is full of water due to the diver allowing water to enter the mouthpiece (as happens, for example, when using a SCUBA regulator), the water is more difficult to purge out because of the 180 degree bend. Also, with any dry snorkel, suction is created as the diver descends due to increasing water pressure with depth. At some depth, say 20 feet (about 10 psi), the pressure differential can become painful to the diver's tongue which may be used to block the mouthpiece opening. Additionally, a snorkel of this design is generally dedicated as a dry snorkel only and would not be logically converted into a non-dry model.
Another dry snorkel has an annular coaxial float that seals against an umbrella shaped top. The snorkel tube extends straight up from the snorkeler's temple and flow in and out of the snorkel makes a sharp 180 degree bend to enter and exit the snorkel top. When the diver descends, the annular coaxial float moves upward and seals the entry. This snorkel has the same disadvantages as the ping pong ball version except that it is less bulky and does not hook on to seaweed and such. It also has the disadvantage of extending straight up from the temple rather than following the contour of the snorkeler's head and that causes more hydrodynamic drag.
The patent that appears to be most relevant to the invention is U.S. Pat. No. 5,117,817, Vertical Coaxial Multi-tubular Diving Snorkel. The disclosed snorkel is much more complex than the inventive design, but also has the feature of being "clean air" in that air is inhaled through the annular area and is exhaled through the coaxial inner tube. This prior art snorkel is very complex and the breathing resistance is very high.